1. Field of the Invention
This invention relates to inspection devices and, more particularly, to an inspection device which utilizes dual radiation detectors to identify a geometric dimension of a part.
2. Description of the Related Art
Lasers have been known and used for measuring the geometric dimensions of a part. Such techniques as shown in FIG. 1 involve positioning a part in the path of a single laser beam 99 thereby obstructing a portion of the beam. The magnitude of radiation present in unobstructed portions 100, 102 then falls incident upon a singular measuring device which converts the magnitude of radiation present in portions 100, 102 to a voltage value which is proportional to a respective physical dimension. Such a technique is not capable of discerning the concentricity of a part as the effective axis 108 of the part may shift (i.e., a non concentric part) in the beam without affecting the total magnitude of radiation which is incident on the measuring device.
Techniques shown in FIG. 2 have been developed which utilize two non-parallel, preferably co-planar laser beams 200 and 210 and two light measuring devices (not shown) to monitor the magnitude of light present in unobstructed portions 202, 212. The part 203 is positioned in the non-parallel beams so that a first portion incident on part 203 is obstructed; whereas a second portion remains unobstructed. By positioning each laser to produce non-parallel paths through the part, any off-axis dimensional characteristic of the part may be detected as a change in magnitude of radiation present in unobstructed portions 202, 212. Co-planar laser beams are necessary to ensure that each beam is incident at the same cross-section of the part. A non-planar analysis performed by non-planar beams will not produce an accurate measure of the part cross section. Two lasers, two detectors and substantial space is required to accommodate such dual non-parallel laser inspection devices. Therefore, there is a need to reduce the number of lasers and provide a package efficient inspection device. In addition, the dual laser systems are typically mounted on a planar structural member in attempt to produce co-planar laser beams. Such a mechanical attempt to achieve co-planar beams is very complex and sensitive to physical disturbance resulting in an expensive and unreliable solution. Therefore, there is a need to provide a low cost and reliable inspection device which is capable of inspecting the cross-section of a part using a single laser beam.